To efficiently supply (feed) electric power from an AC power source to a power reception side, a resonance type non-contact power supply system must efficiently transmit the electric power from the AC power source to a resonance system. For such efficient electric power supply by the resonance type non-contact power supply system, the input impedance of the resonance system at a predetermined resonance frequency of the resonance system must be matched with the output impedance of the AC power source (a high-frequency power source). However, if a foreign object exists between a power supply side (a power transmission side) and the power reception side after the impedances have been matched, the impedances become unmatched, which hampers efficient electric power supply.
Conventionally, a non-contact charging apparatus having a power source device incorporating a primary-side high frequency oscillation circuit and a main body electromagnetically connected to the power source device is known. The main body receives secondary output through electromagnetic induction brought about by high frequency output from the high frequency oscillation circuit and charges a storage battery with the secondary output. Japanese Laid-Open Patent Publication No. 2006-115592, for example, proposes determination means for determining whether the main body is attached accurately to the power source device for such non-contact charging apparatuses. Specifically, when the main body is attached accurately to the power source device, a predetermined level of electric power is supplied to a primary coil if impedances are matched as designed. However, the main body may be displaced with respect to the power source device and thus attached inaccurately to the power source device. Also, the main body may be separated from the power source device and thus detached from the power source device. Further, a conductive foreign object may be placed inadvertently in a recess of a main body attachment portion, which is formed in the power source device to receive the main body. In these cases, the determination means of Japanese Laid-Open Patent Publication No. 2006-115592determines that these problems have occurred through a decrease in the electric current flowing in a primary coil, which is caused by unmatched impedances.